Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02334443 2005-12-O1
SURGICAL BLIND RIVETS WITH CLOSING ELEMENTS
FIELD OF THE INVENTION
The present invention relates to a device for attaching a suture, tissue, or
implant
to a bone.
BACKGROUND OF THE INVENTION
The use of blind rivets in non-medical fields is wide spread. Such blind
rivets,
which typically have a closing head consisting of separate and comparatively
widely
spread legs, are known for example from U.S. Patent No. 4,696,610 to Wright
and U.S.
Patent No. 4,580,936 to Francis. These known blind rivets have longitudinal
slits or cuts
near the end of the shaft which form the closing head when the blind rivet is
closed. The
closing heads so formed rest on a large area. These known blind rivets incur
the drawback
that the closing heads are formed by bending the longitudinal legs and, as a
result, the leg
ends are not sharp tines and cannot be pressed into the material to which the
rivet is being
attached. Thus, these types of blind rivets do not prevent the blind rivet
from rotating in
the boreholes of the materials to be connected.
A different non-medical blind rivet is known from British Application No.
2,054,082 of Tucker FastenersTM. This fastener includes a pyramidal shaped
head that
passes through a cylindrical bore.
Other fasteners operate in a manner analogous to a blind rivet. Examples of
these
fasteners include screws, marrow pins, and hip screws. The SeidelTM marrow pin
for the
humerus is fitted with slits at the tip and the slits are spread apart by a
central pin with a
ballhead. In this manner, the legs are bent outward like wings. However, these
legs are
bent only slightly away from the nail. Use of these fasteners to anchor an
implant in
porotic bone is problematic. Often an implant can be affixed to such bone only
by
injecting bone cement into the bone. This procedure can further damage a bone
due to
heat necrosis as the cement hardens. Moreover, the cement no longer can be
removed as
would be required in case of infection.
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Another drawback of these known fasteners is that the anchoring strength is
determined by its diameter. If there is axial overload, a cylinder of bone
equal to the
fastener diameter will be torn out. In healthy bone, the anchoring strength of
bone screws
will be sufficient. But in the case of osteoporosis, in joint zones, or as
regards thin,
shell-like bones, screw affixation often will be inadequate. Larger screws
cannot be used
because of lack of space, or else they destroy the remaining bone even more.
Thus, there exists a need for an improved fastener.
SUMMARY OF THE INVENTION
The present invention relates to an orthopedic fastener for fixing an implant,
suture,
or tissue to a bone. The fastener comprises a blind rivet and a closing
element. The blind
rivet includes a head at a proximal end, a shank connected to the head, and an
anchoring
portion near a distal end. A bore extends through the head and shank from the
proximal end
to the distal end and the bore has a polygonal cross-section through the
anchoring portion.
The closing element has a body with an outer surface and is configured and
dimensioned to
be received in the anchoring portion. The outer surface of at least a portion
of the closing
element distal end has a polygonal cross-section flaring along the
longitudinal axis toward
the closing element distal end. The anchoring portion of the blind rivet
severs into a
plurality of anchoring legs when the closing element is pulled in the bore
toward the blind
rivet proximal end to thereby prevent rotation of the fastener.
The anchoring legs can be spread by the closing elements into a semi-circular
shape
relative to the longitudinal axis to thereby form the closing head of the
blind rivet. This
feature provides a broad rest for instance on the inside bone surface and,
because the
semi-circular shape of the anchoring leg ends rest almost perpendicularly on
the bone
surface, this design offers jaw-like anchoring the closing head. The blind
rivet can be made
of a plastically deforming material, such as pure titanium, a titanium alloy,
or implant-steel,
to enhance the formation of the semi-circular anchoring legs.
In another embodiment of the fastener of the invention, two mutually opposite
ends
of two mutually opposite anchoring legs of the closing element subtend a
distance "L"
which is two to three times the blind rivet's diameter "D". Again this
considerable
widening of the anchoring legs provides a broad rest on the inside bone
surface.
The polygonal cross-section of the bore can include a plurality of corners
that form
rupture sites between the corner and the outer diameter of the shank to
facilitate severing of
the anchoring portion into the anchoring legs. In an exemplary embodiment, the
rupture
sites have a wall thickness between about 1 % and 9% of the outside diameter
of the shank.
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The head of the blind rivet can be integral with the shank. Alternatively, the
head of
the blind rivet is detachable from the shank. If detachable, the rivet head
can include an
inside thread and the shank includes ~a matching outside thread for detachable
coupling of
the head and shank.
The closing element distal end can have a conical cross-section. The distal
end of
the closing element can also have a tip (like a gimlet or awl) for
facilitating insertion of the
closing element in bone. In order to facilitate severing, the anchoring
portion can have a
wall thickness that is between about 1 % and 20% of the outer diameter of the
shank. This
design allows spreading the rivet shank in simple manner into the separate
anchoring
elements by means of the polygonal cone at the closing element. In one
embodiment, the
distal end has a wall thickness that is greater than that of the proximal end
of the blind rivet.
In an exemplary embodiment, the fastener includes a closing pin operatively
associated with the closing element. The closing pin has a first end extending
through the
bore to pull the closing element through the blind rivet toward the proximal
end. The
closing element can be detachably connected to the closing pin. For example,
the closing
pin can be connected to the closing element by a design rupture site which
allows the
closing pin to separate from the closing element. Alternatively, the proximal
end of the
closing element includes a thread and an end of the closing pin includes a
matching thread.
The fastener according to the present invention results in palliation. In use,
the
fastener is insertable through a small borehole and, following affixation,
includes a broad
resting surface on the inner bone surface due to the spread out anchoring
legs. These
anchoring legs can dig into the inner bone surface and thereby prevent the
blind rivet from
rotating.
One advantage offered by the present invention is that the fastener of the
invention
requires only a small borehole in the bone. However, after implantation, the
blind rivet of
the invention broadly rests on the inner bone surface. Moreover and
illustratively in a
manner different from the case relating to a hip screw, the semicircular
anchor-like design
of the anchoring legs and their anchoring in the bone preclude rotation by the
fastener head.
With respect to porotic bones, the spongiosa in joint heads -- if still
present at all -- will not
be mechanically stressed. In other words, the hip screw is situated in a
cavity, and this
feature entails a dislocation of the hip head relative to the hip screw. The
hip screw only
can become functional after it makes contact with the inner bone surface. In
such cases,
however, the interface between screw and bone often is inadequate, so that the
bone screw
may penetrate the hip joint. In the invention on the other hand, the inner
head surface is
used as the interface between implant and bone when using the blind rivet of
the invention
with the semi-circular anchoring legs. In this manner, the surface of contact
with the bone
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is larger and matches optimally on account of the anatomically matching
anchoring legs. If
the blind rivet of the invention is used to anchor a marrow spindle into the
femur head, the
size of the borehole receiving the blind rivet of the invention will only be
about 8 mm. This
feature offers the advantage that in comparison with conventional systems of
marrow-spindles/hip-screws, the diameter of the marrow spindle can be
substantially
reduced in the application of the invention.
In the medical field, the fastener of the invention is applicable almost
universally in
the treatment of bone fractures for which a bone screw or similar fastener is
presently used.
Specifically:
l 0 ~ for porotic bones partly comprising only a very thin cortex, the
fastener of the
invention can replace screws in fastening plates;
~ in the spongiosa, the fastener of the invention can serve as an anchor for
plates,
sutures or to reattach tendons and ligaments (the claws formed when spreading
the
closing head will anchor well into the trabecular structure of the spongiosa);
and
~ in joint heads such as the femur head or the humerus head, the fastener of
the
invention can be used as the anchor of a side plate or of an intramedullary
support
(heretofore large screws have been used to anchor the longitudinal supports,
however these screws anchor less than optimally in the joint heads' porotic
bones).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. I shows a longitudinal section of an embodiment of a fastener according
to the
present invention;
FIG. 2 shows a longitudinal section of a fastener according to the present
invention
with a closing element that differs from that of FIG. I;
FIG. 3 is a cross-section taken along line A-A of FIG. 2;
FIG. 4 is a longitudinal section of a fastener with a closed blind rivet
fixing a bone
plate to a bone;
FIG. S is an elevation of the embodiment of the closed blind rivet shown in
FIG. 4;
FIG. 6 is a longitudinal section of another embodiment of the blind rivet
component
of the fastener according to the present invention;
FIG. 7 is a front view of the blind rivet shown in FIG. 6;
FIG. 8 is a longitudinal section of another embodiment of the blind rivet
component
of the fastener according to the present invention;
FIG. 9 is a longitudinal section of another embodiment of the fastener
according to
the present invention;
FIG. 10 is a front view of the fastener of FIG. 9; and
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FIG. I 1 is a longitudinal section of a femur bone with a marrow spindle,
assembly
sleeve, and a blind rivet according to the present invention.
DETAILED DESCRIPTION OF DRAWINGS
FIG. 1 shows one embodiment of the fastener according to the present
invention.
The fastener includes a blind rivet 1 and a closing element.2. Blind rivet 1
has a
longitudinal axis 3 and consists of a cylindrical rivet shank 8 that runs
parallel to
longitudinal axis 3 and a rivet head 19 rigidly joined to rivet shank 8. A
cylindrical passage
(i.e., a bore) 4 passes coaxially through blind rivet 1. Rivet shank 8 is of
diameter "D" and,
I 0 as a result, the wall thickness "s", defined by the width of passage 4 and
the outside
diameter "D", is such that when closing blind rivet 1 by means of closing
element 2, the
blind rivet can be severed at the closing pan or anchoring part 9 into
anchoring legs 13
(FIG. 4 and FIG. S). The number of anchoring legs 13 corresponds to the number
of edges
of the polygonal cross-section 5 of closing element 2 (FIG. 3). In this
particular
15 embodiment of blind rivet 1, wall thickness "s" of rivet shank 8 amounts to
14% of the
outer diameter "D".
In the embodiment of the fastener of the invention shown in FIG. 1, closing
element
2 is a component of a closing pin 16. At the segment adjoining rear end 12,
closing element
2 is of polygonal cross-section 5 (FIG. 3) flaring toward rear end 12. Blind
rivet 1 will be
20 closed following insertion of closing element 2 which, by tension applied
to closing pin 16,
is pressed into closing part 9 of blind rivet 1. When flaring segment 7 is
pressed inward, the
wall of rivet shank 8 is widened by segment 7 of closing element 2 and is
severed by the
edges of polygonal cross-section 5 into anchoring legs 13. The conical angle
being selected
in such manner that both severing of the rivet shank into separate anchoring
legs and
25 widening of the anchoring legs when closing the blind rivet will be
enhanced. Closing pin
16 can be connected by a design rupture site to closing element 2 to allow
separating this
pin from this closing element after closing blind rivet 1, for instance by
applying twisting
forces.
The embodiment of the fastener according to the present invention shown in
FIG. 2
30 differs from the embodiment of FIG. 1 in that closing element 2 is fitted
with an inside
thread 24 coaxial with longitudinal axis 3 and closing pin 17 is fitted with a
matching
outside thread 23 to allow detachably screwing closing pin 17 - which is a
separate part--
into closing element 2. Following closure of blind rivet 1, closing pin 17 can
be screwed
out of closing element 2 and thereby be removed from closed blind rivet 1.
35 FIG. 3 is a section perpendicular to the longitudinal axis of the closing
element 2. In
this embodiment, the polygonal cross-section S is a square 6 forming four
anchoring Pegs 13
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when closing blind rivet 1. FIG. 3 also shows inside thread 24 of closing
element 2 of the
fastener of the invention embodiment of FIG. 2.
FIG. 4 shows a longitudinal section of a closed blind rivet 1 of another
embodiment
of the invention. Blind rivet 1 connects a bone plate 25 to a bone 26. Cosing
head 14
comprises four anchoring legs 13, of which ends 31 subtend the distance "L".
FIG. 4 also
shows that the distance "L" subtended by ends 3I of anchoring legs 13 is
approximately
triple the diameter "D"of rivet shank 8. F1G. 5 shows an elevation of the
closed blind rivet
1 of FIG. 4 with four anchoring legs 13.
The blind rivet 1 shown in FIG. 6 and FIG. 7 of another embodiment of the
fastener
of the invention differs from the embodiment of FIG. 1 in that bore 4 has a
square cross
section at closing part 9 of blind rivet 1. One advantage of a cross-section
of few polygonal
edges is that the edges are more sharply defined and severing the rivet shank
into separate
anchoring legs and widening these legs when closing the blind rivet is thus
enhanced.
Corners 1 S of bore 4 form design rupture sites between this passage and the
outside
diameter "D" of rivet shank 8 to facilitate severing of shank 8 into anchoring
legs 13 when
blind rivet 1 is being closed. Advantageously, the rupturing sites wall
thickness can be
between 1 % and 10 %, and preferably between 5% and 9 %, of the outside
diameter "D" of
the blind rivet. At the segment of the blind rivet 1 adjoining rivet head 19,
bore 4 is fitted
with an inside thread 22 coaxial with longitudinal axis 3.
The embodiment shown in FIG. 8 has a blind rivet 1 with a rivet head 20 that
is
detachably connected to rivet shank 8. This detachable connection of rivet
head 20 and
rivet shank 8 can be implemented by threads. Accordingly, river shank 8 is
fitted with an
outside thread 27 coaxial with longitudinal axis 3 and rivet head 20 is fitted
with a matching
inside thread 28.
FIG. 9 and FIG. 10 show a further embodiment of the fastener according to the
present invention. Blind rivet 1 does not have a rivet head and consists of a
cylindrical rivet
shank 8 having a longitudinal axis 3 and a bore 4 also coaxial with axis 3. If
the blind rivet
is used as an anchor, for instance as a fastener in the femur head, together
with a side plate
or a marrow spindle or a suture anchor, an embodiment of the blind rivet
without a rivet
head will be appropriate. The design of a headless blind rivet offers the
advantage of deeper
bone penetration during spreading. This "post-slippage" prevents cutting the
spongiosa
when the blind rivet is being spread apart. Closing element 2 is fitted with
an awl 21. The
diameter "d" of awl 21 corresponds to the outside diameter "D" of the blind
rivet 1 and
thereby pre-drilling bone 26 (FIG. 4) is not needed when assembling blind
rivet 1. A gimlet
can be used instead of awl 21.
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FIG. 11 shows an application of blind rivet 1 to lock a marrow spindle 18 (for
instance in a femur bone 29). Marrow spindle 18 is secured axially in the
proximal
direction by inserting blind rivet 1. Closing element 2 is mounted as a
component of
marrow spindle 18 at its distal end 32. To assemble blind rivet 1, it is
clamped between
closing element 2 and a case 30 and is inserted together with the marrow
spindle 18 into the
femur bone 29. By tensioning marrow spindle 18 in the proximal direction and
applying an
opposite retention force to case 30, closing head 14 is shaped at blind rivet
1, which thereby
is locked.
The preferred embodiments disclosed above discuss the present invention using
I0 specific orthopedic procedures; however, the blind rivet can be used almost
universally in
the treatment of bone fractures where presently bone screws are used. While it
is apparent
that the illustrative embodiments of the invention herein disclosed fulfil the
objectives
stated above, it will be appreciated that numerous modifications and other
embodiments
may be devised by those skilled in the art. Therefore, it will be understood
that the
1 S appended claims are intended to cover all such modifications and
embodiments which come
within the scope of the present invention.
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